Rubidium-filled photonics band-gap fibers offer the prospect of performing nonlinear optics at ultralow light levels. Producing a significant vapor density within such fibers is non-trivial, and I will describe recent experiments that are able to produce optical densities exceeding 1000 at room temperature. Through use of this platform, nonlinear optics at the few-photon level is possible either through cross-phase or cross-absorption modulation. Such a system can be employed to realize the recently proposed weak-nonlinearity based quantum computation paradigm and also quantum non-demolition measurement of photon number.